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    Decreased surface defects and non-radiative recombination via the passivation of the halide perovskite film by 2-thiophenecarboxylic acid in triple-cation perovskite solar cells
    (Royal Soc Chemistry, 2022) Kara, Duygu Akin; Cirak, Dilek; Gultekin, Burak
    Organic-inorganic lead halide perovskite solar cells (PSCs) attract great research interest due to their significant device performance and optoelectronic properties. However, reducing charge recombination and efficiency loss due to surface defects of the perovskite layer are still big issues to overcome for PSCs. Herein, we have employed a simple molecule, 2-thiophenecarboxylic acid (2TiCOOH), via post-treatment to passivate the uncoordinated Pb2+ on the perovskite film surface and improve the stability at the perovskite/Spiro-OMeTAD interface. The spectral results illustrate that the 2TiCOOH passivated devices exhibit higher carrier lifetime, charge extraction, and minimized defect induced recombination. Also, solar cells with 2TiCOOH show better charge collection, improved J(SC), FF, and outstanding power conversion efficiency (PCE). In addition, 2TiCOOH passivated solar cells show tremendously stable performance output with less than 1% PCE drop after 100 days. This work provides a facile surface passivation strategy for fabricating highly efficient, low cost, and stable perovskite solar cells, which can be used for large scale technology and commercialization.
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    Rubrene single crystal solar cells and the effect of crystallinity on interfacial recombination
    (Royal Soc Chemistry, 2022) Kara, Duygu Akin; Burnett, Edmund K.; Kara, Koray; Usluer, Ozlem; Cherniawski, Benjamin P.; Barron, Edward J.; Gultekin, Burak
    Single crystal studies provide a better understanding of the basic properties of organic photovoltaic devices. Therefore, in this work, rubrene single crystals with a thickness of 250 nm to 1000 nm were used to produce an inverted bilayer organic solar cell. Subsequently, polycrystalline rubrene (orthorhombic, triclinic) and amorphous bilayer solar cells of the same thickness as single crystals were studied to make comparisons across platforms. To investigate how single crystal, polycrystalline (triclinic-orthorhombic) and amorphous forms alter the charge carrier recombination mechanism at the rubrene/PCBM interface, light intensity measurements were carried out. The light intensity dependency of the J(SC), V-OC and FF parameters in organic solar cells with different forms of rubrene was determined. Monomolecular (Shockley Read Hall) recombination is observed in devices employing amorphous and polycrystalline rubrene in addition to bimolecular recombination, whereas the single crystal device is weakly affected by trap assisted SRH recombination due to reduced trap states at the donor acceptor interface. To date, the proposed work is the only systematic study examining transport and interface recombination mechanisms in organic solar cells produced by different structure forms of rubrene.